Ironwood and its U.S. partner, Forest Laboratories, Inc., recently
submitted a New Drug Application (NDA) for linaclotide to the U.S.
Food and Drug Administration (FDA) for the treatment of irritable
bowel syndrome with constipation (IBS-C) and chronic constipation
(CC). The submission includes efficacy and safety data from a Phase 3
program that comprised four double-blind placebo-controlled clinical
trials and two open-label long term safety studies. A total of more
than 2,800 patients received a once-daily dose of either linaclotide
or placebo across the four placebo-controlled clinical trials: two
trials in patients with IBS-C and two trials in patients with CC. Over
3,200 patients have enrolled in the long term safety studies, and more
than 1,100 of those patients have received linaclotide for at least 12
months.

Ironwood's European partner, Almirall, S.A., is on track to submit a
Market Authorization Application (MAA) for linaclotide to the European
Medicines Agency for IBS‐C in the second half of 2011.

The results of the two Phase 3 clinical trials in patients with CC are
published in this week's New England Journal of Medicine. The
published data show that in clinical trials, treatment with once-daily
dosing of linaclotide over 12 weeks achieved statistical significance
for the primary endpoint of 12-week complete spontaneous bowel
movement (CSBM) overall responder. In both trials, statistical
significance was achieved for all pre-specified secondary endpoints,
which included measures of bloating, abdominal discomfort, and average
weekly CSBMs. In these two Phase 3 clinical trials, the most commonly
reported adverse event was diarrhea. Most events of diarrhea were
reported as mild to moderate. The topline data were first presented at
the Digestive Disease Week annual meeting in May 2010.

Ironwood entered into commercial supply agreements with PolyPeptide
Laboratories, Inc. and Polypeptide Laboratories (Sweden) AB and with
Roche Colorado Corporation, each for the manufacture of the
linaclotide drug substance that will be incorporated into the finished
product for commercialization. Ironwood also entered into an agreement
with Almac Pharma Services Limited to complete the manufacturing
process of linaclotide in the parts of the world outside of the
partnered territories of North America, Europe, Japan, and certain
other Asian countries and to introduce redundancy into the supply
chain within these partnered territories.

Pipeline

Ironwood continues to advance its pipeline, which includes product
candidates and research efforts focused on gastrointestinal disease,
pain and inflammation, respiratory disease, and cardiovascular
disease. In July 2011, Ironwood entered into a collaboration with
Depomed, Inc. to utilize Depomed's Acuform™ gastric retentive drug
delivery technology to enable an Ironwood early stage, non-GC-C
development program directed at a gastrointestinal disorder.

Corporate

Ironwood ended the second quarter of 2011 with approximately $201
million of cash, cash equivalents, and available-for-sale securities.
Ironwood used approximately $42 million of cash for operations for the
six months ended June 30, 2011. Based on its current operating plan,
Ironwood continues to target ending fiscal year 2011 with greater than
$150 million of cash, cash equivalents, and available-for-sale
securities.

Conference Call Information

Ironwood will host a conference call and webcast at 8:30 a.m. Eastern
Time today to discuss its business activities. Individuals interested in
participating in the call should dial (877) 847-5946 (U.S. and Canada)
or (970) 315-0447 (international) using conference ID number 90255369.
To access the webcast, please visit the Investors section of Ironwood's
website at www.ironwoodpharma.com
at least 15 minutes prior to the start of the call to ensure adequate
time for any software downloads that may be required. The call will be
available for replay via telephone starting today at approximately 11:30
a.m. Eastern Time, running through 11:59 p.m. Eastern Time on August 25,
2011. To listen to the replay, dial (855) 859-2056 (U.S. and Canada) or
(404) 537-3406 (international) using conference ID number 90255369. The
archived webcast will be available on Ironwood's website for 14 days
beginning approximately one hour after the call.

About Linaclotide

Linaclotide, an investigational drug, is an agonist of the guanylate
cyclase type-C (GC-C) receptor located on the luminal surface of the
intestine. In preclinical models, linaclotide reduced visceral
hypersensitivity, increased fluid secretion, and accelerated intestinal
transit. The effects on secretion and transit are mediated through
cyclic guanosine monophosphate (cGMP), which is also believed to
modulate the activity of local nerves to reduce pain. Linaclotide is an
orally delivered peptide that acts locally in the gut with no measurable
systemic exposure at therapeutic doses and is intended for once-daily
administration. The efficacy portion of linaclotide's development
program has been completed and supports the recently submitted NDA for
linaclotide for the treatment of irritable bowel syndrome with
constipation (IBS-C) and chronic constipation, as well as the MAA
submission for the IBS-C indication. An issued composition of matter
patent for linaclotide provides protection to 2025. Ironwood and Forest
are co-developing and, if it is approved, will co-promote linaclotide in
the United States. Ironwood has out-licensed linaclotide to Almirall for
European development and commercialization, and to Astellas Pharma Inc.
for development and commercialization in Japan, Indonesia, Korea, the
Philippines, Taiwan, and Thailand.

Based on improved methods used to measure linaclotide content, the
numbers that define the linaclotide dose are being adjusted from 133 mcg
to 145 mcg and from 266 mcg to 290 mcg. These methods are based on
current industry best practices. The adjustment does not reflect a
change in the actual amount of linaclotide used in clinical trials.
These 145 mcg and 290 mcg designations are utilized in the recently
published NEJM article and the recently submitted NDA.

About Irritable Bowel Syndrome with Constipation (IBS-C)

IBS-C is a chronic functional gastrointestinal disorder characterized by
abdominal pain, abdominal discomfort, and bloating associated with
altered bowel habits, and as many as 11 million people in the U.S.
suffer from it. IBS-C can have an impact on daily living. There are
currently few available therapies to treat this disorder.

About Chronic Constipation (CC)

As many as 34 million Americans suffer from symptoms associated with CC
and 8.5 million patients have sought treatment. Patients with CC often
experience hard and lumpy stools, straining during defecation, a
sensation of incomplete evacuation, and fewer than three bowel movements
per week, as well as abdominal discomfort and bloating. There is a high
rate of dissatisfaction with currently available treatments for CC.

About Ironwood Pharmaceuticals

Ironwood Pharmaceuticals (NASDAQ: IRWD) is an entrepreneurial
pharmaceutical company dedicated to the art and science of great
drugmaking. Linaclotide, Ironwood's GC-C agonist, is an investigational
drug for the treatment of irritable bowel syndrome with constipation
(IBS-C) and chronic constipation. The efficacy portion of linaclotide's
development program has been completed and supports the recently
submitted NDA for both indications, as well as the MAA submission for
the IBS-C indication. Ironwood also has a growing pipeline of additional
drug candidates in earlier stages of development. Ironwood is located in
Cambridge, Mass. To learn more, visit www.ironwoodpharma.com.

This press release contains forward looking statements. Investors are
cautioned not to place undue reliance on these forward-looking
statements, including, but not limited to, the timing of the filing of a
Marketing Authorization Application for linaclotide, linaclotide's
potential as a treatment for IBS-C or chronic constipation, our recent
collaboration with Depomed and its potential benefit to our development
pipeline, and our targeted cash-on-hand for 2011. Each forward-looking
statement is subject to risks and uncertainties that could cause actual
results to differ materially from those expressed or implied in such
statement. Applicable risks and uncertainties include the risks that
Almirall's MAA submission does not progress as expected, serious adverse
events arise in patients that are deemed to be definitely or probably
related to linaclotide treatment, the incidence or severity of diarrhea
in patients treated with linaclotide is higher than expected, and
advancements in our development pipeline do not proceed as expected, as
well as risks related to the difficulty of predicting regulatory
approvals, and the acceptance of and demand for new pharmaceutical
products. Applicable risks also include those that are listed in our
Quarterly Report on Form 10-Q for the quarter ended March 31, 2011, in
addition to the risk factors that are listed from time to time in
Ironwood Pharmaceuticals' Annual Reports on Form 10-K, Quarterly Reports
on Form 10-Q, and any subsequent SEC filings. We undertake no obligation
to update these forward-looking statements to reflect events or
circumstances occurring after this press release. These forward-looking
statements speak only as of the date of this press release. All
forward-looking statements are qualified in their entirety by this
cautionary statement.